Idle speed dips after letting off gas - 92 civic d15b7

Hello All,
I have something on my mind that keeps bothering me and so far I could
not find an answer for it. I figured I'd post it and see if I could
get some ideas regarding this.

I have a 92 civic CX (canadian model with D15B7)with 300,000 km.
Car has been running fine, except for the overheating issue I had with
it when engine was under heavy load. I've replaced the head gasket,
got the head machined and pressure tested, flushed rad and cooling
system and that has taken care of overheating.

Ever since this has been done, I've been having an intermittent problem
where if I rev the engine and then abruptly let go of the gas so that
the throttle closes abruptly (while driving or at idle, in neutral or
with clutch depressed, does not matter), idle RPM will drop below 500,
making it sound like it's trying to stall. It will struggle at this
RPM for about 5 sec and return back to normal Idle of about 650 RPM
where it runs just fine. It keeps doing this even after the car has
warmed up.

Engine by itself runs just fine at other rpm, there are no signs of it
missing.

I've got few things I am going to check within the next couple of days,
such as timing belt tension, ignition timing, disconnecting air intake
pipe, etc. I am just curious if you guys have any other ideas or
suggestions about what I can try to do or possibly try to eliminate
some of the possibilites.

I would greatly appreciat some input on this.
Thank You and Best Regards,
BRadley

 

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Your ECU got 'retrained' after the work, and now it's responding
different. Hondas kill the injectors when not needed, and my old CR-V
did that just like yours. Looks wierd, eh?
You could search Google for info about honda ecu training.

'Curly'